On Fri, May 04, 2012 at 01:26:45PM +0900, Minchan Kim wrote:[...]> > be useful for different use cases.> > Why should we do it in kernel side?

Because currently you can't do this in userland, see below. Todaythis would be effectively the same as constantly reading /proc/vmstat,which is surely not friendly performance/context switches/batterywise.

> If vmevent will have VMEVENT_ATTR_[FILE|MOCK|DIRTY|WRITEBACK|SHMEM|ANON|SWAP]_PAGES> and so on which is needed by calculation, we can calculate it in userspace without> forking /proc/vmstat to see it. So I think there is no problem to do it in userspace.

There are two problems.

1. Originally, the idea behind vmevent was that we should not expose all these mm details in vmevent, because it ties ABI with Linux internal memory representation;

2. If you have say a boolean '(A + B + C + ...) > X' attribute (which is exactly what blended attributes are), you can't just set up independent thresholds on A, B, C, ... and have the same effect. (What we can do, though, is... introduce arithmetic operators in vmevent. :-D But then, at the end, we'll probably implement in-kernel forth-like stack machine, with vmevent_config array serving as a sequence of op-codes. ;-)

If we'll give up on "1." (Pekka, ping), then we need to solve "2."in a sane way: we'll have to add a 'NR_FILE_PAGES - NR_SHMEM -<todo-locked-file-pages>' attribute, and give it a name.